This project studies the pathophysiological and hormonal regulation of membrane transport systems and the mechanisms by which age-dependent changes perturb physiological control systems and, thus, contribute to the failure to maintain homeostasis in the aged. Findings include: (1) sodium/proton exchange activity in rat renal brush border membrane vesicles was increased in metabolic acidosis, and this response required an intact adrenal gland or glucocorticoid supplements; (2) glucocorticoids acted directly on renal cells in culture to inhibit phosphate uptake; (3) renal membrane transport systems were altered in the streptozotocin-diabetic animal; (4) peptide mapping and identification of the amino-terminal residues of the peptides of the catalytically active and inactive forms of the renal membrane enzyme maltase were indistinguishable, suggesting the close homology of the "young" and the "aged" form of the enzyme; (5) a technique was developed for the purification to homogeneity of a phosphlipid + lipid + calcium-dependent protein kinase, and the activity of the enzyme was characterized; (6) the hormonal responses of a primary cultured renal cell was characterized; (7) the control of physiological responses in parotid cell aggregates was described.